1. Field of the Invention
The present invention relates to soap bar compositions having enhanced structural integrity, hardness, slough and wear- and crack-resistant properties.
2. Discussion of the Prior Art
The solubility of soaps in water is generally very high, especially when they contain high levels of salts of unsaturated fatty acids (oleate and linoleate). Soaps derived from high levels of coconut oil have high wear properties, and they possess poor slough characteristics. These soaps produce good lather and are resistant to crack; however, rate of wear and slough properties are important attributes in a soap bar. Structurants or fillers have been commonly used in detergent bars to improve the properties of the bar. They are used to provide structural integrity, as well as to improve the physical properties of the soap bars in which they are incorporated. For example, electrolytes (sodium chloride) and various polymers have been added to soap bars to improve the wear characteristics by salting out the liquid phase in the bar. However, the resulting soaps have poor lather and increased tendency to crack.
Tetrasodium pyrophosphate (TSPP) has been previously used in detergent bar formulations as a filler. It has low solubility in water (7-8% at room temperature), high transition temperature (80.degree. C.) and absorbs water (60% of its weight). On recrystallization, TSPP forms long needle and hexagonal platelets.
U.S. Pat. No. 2,686,761, for example, discloses the addition of TSPP to soap bar compositions containing high moisture levels, i.e., greater than 20% by weight. The TSPP is combined with the high moisture content soap in the crutcher; however, the mixture must be subjected to rigorous kneading, shearing and compacting to result in a "salting-out" of the molten soap and water so as to produce a bar having milled soap properties and which is waxy, translucent and predominantly in the beta phase.
The resulting bar has a high total water content, however, at a cost of reduced soap content. In addition, the presence of excess moisture in the bar leads to an increased tendency to crack. Those skilled in the art will appreciate that the TSPP functions as an inert filler in the soap bar disclosed in U.S. Pat. No. 2,686,761, thereby enabling the provision of a composition containing more water and less soap with inferior structural properties.
U.S. Pat. No. 4,308,158 relates to a synthetic surfactant composition containing a builder which comprises a mixture of alkali metal orthophosphate, alkali metal pyrophosphate and alkali metal tripolyphosphate.
U.S. Pat. No. 3,639,286 discloses the addition of an alkali metal trimetaphosphate to a synthetic detergent bar or cake to absorb the water content thereof such that the final water content is as water of crystallization of the tripolyphosphate salt.
U.S. Pat. No. 3,494,869 describes a superfatted soap bar containing an acidulating agent which may comprise a phosphorous acid or a strong acid salt thereof. The acidulating agent is present to react with the constituent soaps to form free fatty acids in situ.
U.S. Pat. No. 2,868,731 discloses the inclusion of TSPP in non-soap detergent bars to function as a "filler."
U.S. Pat. Nos. 2,970,116 and 3,274,119 relate to a transparent soap bar having a high moisture content and containing an electrolyte including sodium tripolyphosphate to salt out the water.
U.S. Pat. No. 3,370,015 discloses strong, fast-dissolving detergent tablets containing a hydratable condensed phosphate such as TSPP.
U.S. Pat. No. 4,297,230 describes a noncrystallizing transparent soap bar containing 4 to 20% potassium soap and an electrolyte which may comprise tetrasodium pyrophosphate.
U.S. Pat. No. 3,344,076 relates to detergent tablets or briquettes containing at least 20% by weight of a phosphate component (tetrapotassium pyrophosphate or pentasodium or pentapotassium tripolyphosphate). The tablets are designed to have a high rate of disintegration and solubilization in washing machines.
U.S. Pat. No. 3,798,181 discloses an enzymatic detergent bar useful for washing laundry and containing, as a builder, tetrapotassium pyrophosphate.
It is an object of the present invention to provide a soap detergent bar having a low moisture content and enhanced structural integrity, hardness, slough and wear- and crack-resistant characteristics.